The present invention relates generally to pumping devices, and more particularly refers to petroleum pumping devices used especially for offshore production fields.
Pumping devices of this type are already known which contain a drive device which, with the aid of a flexible connection attached to a train of rods of the production well, imparts to the rods a reciprocating movement whose frequency and amplitude are adjustable. The drive device usually comprises a hydraulic motor, on the output shaft of which is fastened a toothed wheel meshing with a flexible connection, which usually comprises a link chain, the motor being fed by a variable delivery hydraulic pump the delivery of which is controlled in accordance with a cycle determined by the required movement of the train of rods. The end of the chain opposite to the train of rods is then fixed to a counterweight, the value of which is calculated in dependence on the weight of the train of rods, and in dependence on the pumping force to be supplied, that is to say the mass of the column of fluid to be pumped. This counterweight is generally equivalent to the sum of the mass of the train of rods and half that of the column of fluid pumped.
A counterweight of this kind makes it possible to reduce considerably the motive power required, but because of its mass (up to 5 metric tons in certain cases) and its stroke (which is that of the pump, that is to say of the order of from 2 to 10 meters) it entails disadvantages, because it increases considerably the size of the pumping apparatus.